1. Field of the Invention
This invention relates to a DC motor control system and method, more particularly to a DC motor control system and method which controls a DC motor for driving a suction pump used in cleaning a recording head.
2. Prior Art
Conventionally, an ink jet recording apparatus is known which automatically performs a cleaning operation to ensure a positive printing operation after replacement of ink cartridges for holing ink and at the same time reliably fill a recording head of the apparatus with ink.
The term xe2x80x9ccleaning operationxe2x80x9d is used herein to mean sucking of ink from ink reservoirs of an ink cartridge into a cap arranged in a non-printing area of the apparatus through the nozzles of the recording head to thereby prevent the nozzles from being clogged and eliminate bubbles in an ink passage that prevent the nozzles from operating properly.
When the cleaning operation is carried out, the recording head is hermetically sealed by a cap, and negative pressure is created within a gap formed between the recording head and the cap, by a suction pump. This causes ink to be sucked from within the recording head into the cap for effecting the cleaning of the print head.
In the conventional ink jet recording apparatus, a stepping motor is used for performing the accurate control of the amount of rotation of a motor for driving the suction pump, that is, the accurate control of the amount of suction of ink.
Assuming that a recording apparatus employs a battery as a drive source, however, if the voltage of the battery becomes lower than a predetermined value of voltage required for driving the stepping motor, the apparatus ceases to function properly, and get out of control. This makes it impossible to carry out the accurate control of the amount of suction of ink.
It is a first object of the invention to provide a DC motor control system which is capable of carrying out an accurate rotation control of a DC motor even when the power supply voltage has been lowered.
It is a second object of the invention to provide a method of controlling rotation of a DC motor, which is capable of carrying out an accurate rotation control of the DC motor even when the power supply voltage has been lowered.
To attain the first object, according to a first aspect of the invention, there is provided a motor control system for carrying out rotation control of a DC motor, comprising:
detection means for detecting rotations of the DC motor and outputting a detection signal indicative of a number of the detected rotations of the DC motor; and
motor stop control means which carries out stop control for stopping the DC motor by braking rotation of the DC motor when the number of the detected rotations of the DC motor indicated by the detection signal has reached a predetermined number.
To attain the first object, according to a second aspect of the invention, there is provided a DC motor control system for carrying out rotation control of a DC motor, comprising:
detection means for detecting rotations of the DC motor and outputting a pulse signal having a number of pulses corresponding in number to the number of the detected rotations,
determination means for determining whether or not a count of the pulses of the pulse signal is equal to a reference count;
drive current control means for controlling a drive current supplied to the DC motor by effecting pulse width modulation control of the drive current; and
motor stop control means which carries out stop control, via the drive current control means, for stopping the DC motor by braking rotation of the DC motor when the count of the pulses of the pulse signal becomes equal to the reference count.
Preferably, when the DC motor starts to rotate, the drive current control means maintains a pulse width at its maximum value, thereby maintaining the drive current at its maximum amount during a time period from a point in time at which the DC motor starts to rotate to a point in time at which the count of the pulses reaches a predetermined initial count.
Preferably, the detection means comprises a rotary encoder, and wherein the pulse signal has one or a plurality of pulses per one rotation of the DC motor.
Preferably, the DC motor control system includes rotational speed detection means for detecting a rotational speed of the DC motor by measuring an interval from one timing of transition from one signal level to another signal level and next timing of the transition from the one signal level to the another signal level, and rotational speed comparison means for comparing the rotational speed of the DC motor detected by the rotational speed detection means with a reference rotational speed, and the drive current control means controls the drive current based on a result of the comparison.
More preferably, the DC motor control system includes reference rotational speed data storage means for storing reference rotational speed data representative of the reference rotational speed.
Further preferably the reference rotational speed data storage means includes normal rotation reference rotational speed data storage means for storing the reference rotational speed data for normal rotation of the DC motor, and reverse rotation reference rotational speed data storage means for storing the reference rotational speed data for reverse rotation of the DC motor.
Preferably, the motor stop control means includes brake time period storage means for storing in advance a brake time period over which rotation of the DC motor is braked, and drive current supply stop means for stopping supply of the drive current to the DC motor after a lapse of the brake time period.
To attain the second object, according to a third aspect of the invention, there is provided a method of controlling rotation of a DC motor, comprising the steps of:
detecting rotations of the DC motor and outputting a detection signal indicative of a number of the detected rotations of the DC motor; and
carrying out stop control for stopping the DC motor by braking rotation of the DC motor when the number of the detected rotations of the DC motor indicated by the detection signal has reached a predetermined number.
To attain the second object, according to a fourth aspect of the invention, there is provided a method of controlling rotation of a DC motor, comprising the steps of:
detecting rotations of the DC motor and outputting a pulse signal having a number of pulses corresponding in number to the number of the detected rotations,
determining whether or not a count of the pulses of the pulse signal is equal to a reference count;
controlling a drive current supplied to the DC motor by effecting pulse width modulation control of the drive current; and
carrying out stop control for stopping the DC motor by braking rotation of the DC motor when the count of the pulses of the pulse signal becomes equal to the reference count.
Preferably, the step of controlling the drive current includes, when the DC motor starts to rotate, maintaining a pulse width at its maximum value, thereby maintaining the drive current at its maximum amount, during a time period from a point in time at which the DC motor starts to rotate to a point in time at which the count of the pulses reaches a predetermined initial count.
Preferably, the DC motor includes a rotary encoder for generating the pulse signal, and the pulse signal has one or a plurality of pulses per one rotation of the DC motor.
Preferably, the method further includes the steps of detecting a rotational speed of the DC motor by measuring an interval from one timing of transition from one signal level to another signal level and next timing of the transition from the one signal level to the another signal level, and comparing the detected rotational speed of the DC motor with a reference rotational speed, and the step of controlling the drive current includes controlling the drive current based on a result of the comparison.
Preferably, the step of carrying out the stop control comprises the steps of storing in advance a brake time period over which rotation of the DC motor is braked, and stopping supply of the drive current to the DC motor after a lapse of the brake time period.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.